A stoichiometric mixture of evaporating materials for ZnAl2Se4 single-crystal thin films was prepared in a horizontal electric furnace. These ZnAl2Se4 polycrystals had a defect chalcopyrite structure, and its lattice constants were a0= 5.5563 A and c0= 10.8897 A.To obtain a single-crystal thin film, mixed ZnAl2Se4 crystal was deposited on the thoroughly etched semiinsulating GaAs(100) substrate by a hot wall epitaxy (HWE) system. The source and the substrate temperatures were 620 oC and 400 oC, respectively. The crystalline structure of the single-crystal thin film was investigated by using a double crystal Xray rocking curve and X-ray diffraction ω-2θ scans. The carrier density and mobility of the ZnAl2Se4 single-crystal thin film were 8.23 × 1016 cm.3 and 287 m2/vs at 293 K, respectively. To identify the band gap energy, the optical absorption spectra of the ZnAl2Se4 single-crystal thin film was investigated in the temperature region of 10-293 K. The temperature dependence of the direct optical energy gap is well presented by Varshni's relation: Eg(T) = Eg(0) . (αT2/T + β). The constants of Varshni's equation had the values of E g(0) = 3.5269 eV, α = 2.03 × 10.3 eV/K and β = 501.9 K for the ZnAl2Se4 single-crystal thin film. The crystal field and the spin-orbit splitting energies for the valence band of the ZnAl2Se4 were estimated to be 109.5 meV and 124.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that splitting of the Δso definitely exists in the Γ5 states of the valence band of the ZnAl2Se4/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-exciton for n = 1 and C21-exciton peaks for n = 21.